Method for deposition of inert barrier coating to increase corrosion resistance

ABSTRACT

The present invention reduces corrosion rates on metal surfaces, such as the interior surfaces of gas flow control components by depositing a chemically inert layer on the metal surface of the component and other associated parts of the component that are exposed to corrosive gases. The disclosed method provides for depositing a relatively chemically inert thin film such as silicon dioxide along the gas exposed surface areas of the metal surface thereby enhancing corrosion protection to the metal surfaces. The present invention can be used to deposit a chemically inert thin film at locations inside components that are outside a direct line of sight and at locations normally unreachable by a gas flowing through the components. The present invention does not require a vacuum system for the deposition of the corrosion-resistant thin film.

RELATED APPLICATIONS

[0001] A provisional application corresponding to the subject matter ofthis application was filed on Oct. 18, 2002, and assigned Serial No.60/419,146. Applicants claim the benefit of the filing date of saidprovisional application.

FIELD OF THE INVENTION

[0002] The invention relates to chemical deposition and moreparticularly to the chemical deposition of an inert layer on the metalparts of components and associated adapted to be exposed to corrosivegases when in use.

BACKGROUND OF THE INVENTION

[0003] Many of the gases used in manufacturing tend to corrode metalparts of components and equipment. For example, gases used inmicroelectronic fabrication such as in thin film deposition and etchingare highly corrosive gases. For example, chlorine (Cl₂), hydrochloricacid (HCl) and fluorine (F₂) are used in plasma etching, anddichlorosilane (SiH₂Cl₂), germane (GeH₄), and silicon tetrachloride(SiCl₄) are used in plasma deposition. The corrosive properties of thesegases limit the life of the components and equipment, such as forexample, gas flow control regulators, used to control the gases. Thereaction products that are created when the gases interact with thesurface of the gas flow control component may introduce contaminantsinto the gas stream. The continuous flow of these corrosive gasesthrough a gas flow control component greatly reduces the life of thecomponent. Thus, it is desirable and advantageous to provide acontinuous coating of an inert, corrosion resistance substance on thesurfaces of components that are exposed to corrosive gases to extend thelife of such components.

SUMMARY OF THE INVENTION

[0004] The present invention is intended to reduce corrosion rates onmetal parts and components, especially gas flow control components, bydepositing a chemically inert layer on the metal parts. Thus, the metalparts of a flow control component and other associated parts ofcomponents that are exposed to corrosive gases are protected. Thedisclosed method provides for depositing a relatively chemically inertthin film along the metal parts adapted to be exposed to corrosivegasses thereby enhancing corrosion protection to the metal surfaces. Thepresent invention can be used to deposit a chemically inert layer atlocations inside flow control components that are outside a direct lineof sight and at locations unreachable by a gas flowing through the flowcontrol components. In addition, in a preferred embodiment, the presentinvention does not require vacuum systems for the deposition of thecorrosion-resistant layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a block diagram illustrating the basic process forcreating silicon dioxide layer.

[0006]FIG. 2 is a block diagram illustrating a method for coating a gasflow component with a layer of silicon dioxide that uses a flowconfiguration in the formation of the silicon dioxide.

[0007]FIG. 3 is a block diagram illustrating a method of coating acomponent with silicon dioxide using the component as a mini-chamberthat does not require a vacuum chamber.

DETAILED DESCRIPTION

[0008] The inventive methods increase the corrosion resistance ofcomponents having interior surfaces by coating the inside surface of thecomponent with SiO₂ (silicon dioxide or silica). In particular, lowtemperature chemical vapor deposition of SiO₂ from the thermaldecomposition of commercially available, low toxicity reagents producessilicon films that have good uniformity and film properties.

[0009] DADBS is a preferred precursor of SiO₂, as it is relatively safeand easy to handle, and it is liquid at ambient conditions. The basicreactions used to create a layer of SiO₂ from a precursor are describedbelow. These basic processes are similar to the processes used insemiconductor manufacturing, and the resulting coating on the insidesurface of the treated components is contaminant-free to a levelcompatible to the semiconductor industry. The inventive methods areparticularly adapted for, but not limited to, treating gas flow controlcomponents such as regulators, valves and the like through whichcorrosive gases may flow.

[0010] Basic Process for Forming Silicon Dioxide A preferred method ofacquiring the Silicon Dioxide (SiO₂) needed to create a silicon dioxidethin film is to decompose a SiO₂ precursor such as DADBS(diacetoxyditertiarybutoxysilane), or TEOS (tetraethoxysilane). DADBSdeposits SiO₂ films at temperatures ranging from 400° C. to 600° C. Theformation of SiO₂ from these precursors is due to the thermaldecomposition of the precursor in a homogenous gas-phase reactionfollowed by a heterogeneous surface reaction with a metal surface, suchas the inner surface of a gas flow control component. The process isshown in FIG. 1.

[0011] As shown in FIG. 1, the process starts with precursor 10.Precursor 10 is thermally decomposed 15 into an intermediate product I(20) and, typically, byproducts R (25). I is typically a gas phaseintermediate containing Si and O₂. By-product R is typically a gas-phaseorganic by product. For example, when using DADBS as the precursor, thegas-phase reaction during thermal decomposition proceeds as follows:

SiC₁₂H₂₄O₆→I+R₁ (thermal decomposition)

[0012] where I is an intermediate species in the gaseous phasecontaining Si and oxygen, and R₁ is an organic by-product also in thegas phase.

[0013] As shown in FIG. 1, the intermediate I adsorbs 30 onto a surfaceat a vacant surface site. This can be shown as:

I+*→I^(*) (surface adsorption)

[0014] where * represents a vacant surface site, and I^(*) representsthe surface site with the adsorbed intermediate I. The adsorbedintermediate I* (35) thermally decomposes on the surface 40 to form SiO₂(45) and, typically, a volatile organic by-product 50 in the gas phase.This process proceeds as follows:

I^(*)→SiO₂+R₂+* (decomposition of intermediate to form SiO₂)

[0015] By-product R₂(50) typically may be readily pumped out or simplyflushed out. Therefore, after pumping out any excess by-products, asilicon dioxide layer will be left deposited on surface *.

[0016] For DADBS, all reactions needed to deposit the SiO₂ will occur atapproximately 450° C. The reaction temperature may be reduced evenfurther by mixing in oxygen or ozone, although as oxygen is preferablypresent in the reagents used in the process. It is therefore notnecessary to add any oxygen during the process.

[0017] Process for Silicon Dioxide Deposition

[0018] In current systems used to form a dielectric layer insemiconductor fabrication, deposition of SiO₂ is typically performed ina flowing vacuum system. However, this methodology has not been used tocoat metal surfaces for corrosion protection of metal surfaces.

[0019] As shown in FIG. 2, component 110 having interior surfaces to betreated, such as, for example, a gas flow control regulator or valve, isconnected to vacuum pump 120, loaded into heating oven 130, pumped downto a pressure of approximately 1 mTorr and heated until the inner wallsof component 110 reach a desired deposition temperature. A precursor,for example DADBS, is placed in a container 150. For DADBS, reactionsneeded to deposit SiO₂ will occur at approximately 450° C., but thedeposition temperature may be reduced by mixing in oxygen. The DADBS isin liquid form at ambient conditions but is easily evaporated by heatingthe container to temperatures about 50-100° C. Container 150 may be around bottom stainless steel flask, for example. Before deposition, thevapor on top of the DADBS liquid is pumped out through a by-pass line145. Container 150 has a flow controller 155 such as a needle valve tocontrol the vapor flow rate. The DADBS vapor is introduced into heatedcomponent 110 with the flow rate monitored by a flow meter 140. At theend of the deposition process, the DADBS vapor flow is shut off and theheated component pumped out using pump 120 to remove residual gases.Pump 120 and valve 121 are also used to maintain vacuum integrity.

[0020] This is a complicated process requiring careful control of flowrate and in maintaining vacuum integrity while heating to approximatelyat least 450° C. and preferably approximately 500° C. However lowertemperatures may be used if oxygen is added.

[0021] Component Used as Mini-Chamber

[0022] An alternative, preferred, embodiment for the deposition of SiO₂on components having interior surfaces, such as a gas flow controlcomponent is shown in FIG. 3. In this preferred embodiment, a vacuumsystem is not required. By this process, small diameter ports or otherrecesses inside the components that are not within the flow path arecoated during the process.

[0023] As shown in FIG. 3, a measured quantity of the SiO₂ precursor 210is introduced in the component itself 220, which may be a gas flowcontrol regulator or valve having interior surfaces or parts. This isdone by simply adding a measured volume of DADBS, or other SiO₂precursor, to or within the component body 220 and sealing it so thatthe DADBS remains trapped inside it while the temperatures needed toinitiate the decomposition reaction and SiO₂ deposition are reached. Thecomponent 220 is sealed, using seal 223 for example, therebytransforming the component into a sealed mini-chamber. The component maybe sealed using brass connections, for example. It is possible for a gasflow component to act as a mini-chamber, because gas flow controlcomponents, such as regulators, can withstand many atmospheres ofinternal gas pressure. When this mini-chamber is heated to about 450° C.and preferably approximately 500° C. in oven 130, the component isfilled with high pressure DADBS, or other precursor. The precursorstarts to evaporate and fill the component at temperatures below 100° C.As the temperature of the inner walls of component 220 increases to 450°C., the DADBS molecules collide with the inner walls of component 220,thereby forming a thin film of SiO₂ on the inner wall surface upon theirdecomposition. The reaction process may be carried out at temperaturesbetween approximately 400° C. and 600° C.

[0024] Coating of intricate and/or dead ended flow paths or recesses isassured by placing the precursor at or near those locations.

[0025] In this preferred embodiment of the present invention, severaladvantages are achieved. The process provides for a relativelychemically inert surface that enhances corrosion protection for thesurface. The coating is deposited uniformly on inside surfaces and partof a flow control component with no need for a direct line of sight, andcan be deposited at surface locations otherwise unreachable by a gasflowing through the flow control component. The coating can be depositedat temperatures less than 500° C., and generally in the range of 450° C.to 600° C. One embodiment of the inventive process does not require avacuum system for deposition.

[0026] In addition, the inventive process involves materials that do notpresent serious hazards to an operator, and technicians can perform theinventive process safely and with high reliability.

[0027] While the invention has been described in conjunction withspecific embodiments thereof, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, the preferred embodiments of the invention as setforth herein, are intended to be illustrative, not limiting. Variouschanges may be made without departing from the spirit and scope of theinvention as set forth herein and defined in the claims.

What is claimed is:
 1. A system for coating metal surfaces with a thinfilm of corrosion resistant material, comprising: means for heating asurface to be coated; means for exposing the surface to be coated to acorrosion resistant precursor gas; and means for coating the surfacewith a thin film of corrosion resistant material when the corrosionresistant precursor gas thermally decomposes and forms absorbate on themetal surface.
 2. The system of claim 1, wherein said surface to becoated is an inner surface of a component.
 3. The system of claim 2,wherein the component is a gas flow control component.
 4. The system ofclaim 2, wherein said means for heating the surface to be coatedcomprises an oven in which the component is placed.
 5. The system ofclaim 1, wherein said means for exposing the surface to be coated to acorrosion resistant precursor gas comprises means for pumping vapor outof a container containing a precursor.
 6. The system of claim 5, whereinthe precursor is initially in liquid form, and the container is heatedto cause the precursor to change to vapor form.
 7. The system of claim5, said means for exposing the surface further includes a flowcontroller to control the rate of vapor flow to the surface to becoated.
 8. The system of claim 1, wherein said means for coatingcomprises means for controlling the pressure of the system duringcoating.
 9. The system of claim 1, wherein the surface to be coated isan interior surface of a gas flow control component and furtherincluding means for controlling the pressure in the gas flow controlcomponent.
 10. The system of claim 9, wherein said means for controllingthe pressure in the gas flow control component includes means forpumping a pressure down to about 1 mTorr.
 11. The system of claim 1,wherein said precursor is a SiO₂ precursor gas.
 12. The system of claim11, wherein said precursor gas is DADBS.
 13. The system of claim 1,wherein the metal surface to be coated is the interior surface of a gasflow control component, and said means for exposing the surface to acorrosion resistant gas comprises placing a precursor inside the gasflow control component.
 14. The system of claim 13, wherein said meansfor coating the surface further comprises means for controlling thepressure in the gas flow control component.
 15. The system of claim 14,wherein the gas flow control component is a sealed unit, said unit beingsealed after a precursor is placed inside the unit.
 16. The system ofclaim 1, wherein the thin film of corrosion resistance material iscomprised of silicon dioxide.
 17. A method of coating the interiorsurface of a component with a corrosion resistant thin film, comprisingthe steps of: placing a predetermined amount of a precursor within thecomponent; sealing the component; and heating the component sufficientlyto cause the precursor to thermally decompose and form a thin film onthe interior surface of the component.
 18. The method of claim 17,additionally comprising the step of placing the component inside anoven, wherein said oven is heated to a temperature of at least 100° C.19. The method of claim 17, wherein said precursor is a SiO₂ precursor.20. The method of claim 19, wherein said precursor is DADBS.
 21. Themethod of claim 17, wherein said corrosion resistant thin film iscomprised of silicon dioxide.
 22. The method of claim 17, wherein saidcomponent is heated to between approximately 400° C. and 600° C.
 23. Themethod of claim 17, wherein said component is a gas flow controlcomponent.
 24. The method of claim 17, wherein said precursor is mixedwith an oxygen or ozone producing agent.
 25. The method of claim 17,wherein the thin film is formed by vapor deposition.
 26. A corrosionresistant component, wherein at least one inner surface of saidcomponent is coated with a thin film of silicon dioxide, wherein saidsilicon dioxide thin film is formed by a flow of an evaporated precursorthrough the component when the component is in an oven, the flow of theevaporated precursor controlled by a vacuum pump that maintains vacuumpressure.
 27. The corrosion resistant component of claim 26, whereinsaid precursor is DADBS in liquid form.
 28. The corrosion resistantcomponent of claim 27, wherein said flow of the evaporated precursor iscreated by pumping vapor from a container of liquid DADBS, whereby thecontainer is heated to a sufficient level to evaporate the DADBS. 29.The corrosion resistant component of claim 26, wherein a rate of flow ofsaid evaporated precursor is controlled by a flow controller.
 30. Thecorrosion resistant component of claim 26, wherein said component is agas flow control component.
 31. A corrosion resistant component, havingat least one inner surface of said component coated with silicondioxide, said coating of silicon dioxide being formed from apredetermined amount of a precursor placed inside said component afterwhich the component is sealed and heated to a temperature such that theprecursor evaporates and said corrosion resistant coating is formed whensaid evaporated precursor reacts with the at least one inner surface ofthe component thereby depositing silicon dioxide on the at least oneinner surface.
 32. The corrosion resistant component of claim 31,wherein said precursor is DADBS in liquid form.
 33. The corrosionresistant component of claim 31, wherein said component is initiallyheated to at least 100° C., and thereafter the temperature of thesurface to be coated is heated to at least 400° C.
 34. The corrosionresistant component of claim 33, wherein said component is heated to atemperature between 450° C. and 600° C.
 35. The corrosion resistantcomponent of claim 34, wherein said component is a gas flow controlcomponent having inner surfaces to be coated.